MIC2, TDT, BCL-2, AND CD34 EXPRESSION IN PARAFFIN-EMBEDDED HIGH-GRADELYMPHOMA ACUTE LYMPHOBLASTIC-LEUKEMIA DISTINGUISHES BETWEEN DISTINCT CLINICOPATHOLOGICAL ENTITIES

We propose that 12E7 (CD99) expression, along with TdT, bcl-2, and CD3 4 reactivity in lymphoblastic lymphoma (LyL)/acute lymphoblastic leuke mia (ALL), distinguishes this group of neoplasms from small noncleaved cell lymphomas (SNCLs) in both pediatric and adult patients, thereby narrowing the differential diagnosis of high-grade non-Hodgkin's lymph omas and acute lymphoblastic leukemias in paraffin sections. 12E7 (CD9 9) is one of a group of available antibodies that recognizes the produ ct of the mic-2 gene, which was originally identified in ALL. Despite this, most clinicopathological research has focused on the reactivity of 12E7 in a subset of the small round cell tumors of childhood. Altho ugh TdT is widely used in the subtyping of blastic leukemias, its use in the distinction of high-grade lymphomas in paraffin sections has be en limited. We collected 24 cases of LyL/ALL (13 B-cell and 11 T-cell) and 15 cases of SNCL from 1984 through 1993. We confirmed the diagnos es using morphology and analysis of immunologic data. We performed imm unohistochemistry with the 12E7 antibody, TdT, bcl-2, and CD34 on form alin-fixed, paraffin-embedded material. The patients' ages ranged from 4 to 81 years; nine of the study patients were children. Sixteen of t he 24 LyL/ALLs stained with 12E7. In contrast, none of the 15 cases of SNCL reacted with this antibody (chi-square P < .0001). A larger perc entage of T-cell LyL/ALLs reacted with 12E7 than did B-cell LyL/ALLs ( 82% v 54%). Sixteen of 20 LyL/ALLs reacted with the anti-TdT antibody, as compared with none of 11 SNCLs (chi-square P < .0001). Six LyL/ALL s were CD34 positive (of 23), and none of the SNCLs were CD34 positive (0 of 12) (chi-square P =.0519). Bcl-2-positive cases were found amon g both LyL/ALLs and SNCLs, although they were more prevalent among LyL /ALLs (92% v 25%; chi-square P < .0001). When one considers the differ ential diagnosis of a high-grade lymphoma/acute lymphoblastic leukemia , positive reactions with 12E7, TdT, bcl-2, and CD34 support the diagn osis of LyL/ALL over SNCL. Moreover, we present data that suggests tha t evaluating for TdT in formalin-fixed paraffin-embedded tissue is a m ore sensitive test than using either 12E7, bcl-2 or CD34 alone. Copyri ght (C) 1997 by W.B. Saunders Company.